I know how you feel. It probably will not be the last time you get so frustrated with the car...
Let it sit, work on something else, maybe take it to a transmission shop and some input?
I bought a used 95 motor and T56, have had it for 4 years and not yet tried 5th and 6th, so cross your fingers I could have the same problem.
One good note, you now know a lot about this transmission, you WILL get it figured out.. and if you ever have another trans problem you will probably solve it quickly...